Our goal is to understand structure-property relationships of ion-conducting membranes and ultimately design superior materials for electrical chemical technologies. This is achieved through control of the membrane’s chemical microstructure, in conjunction with evaluation of properties such as ion conductivity, water retention and transport, and mechanical stability, chemical stability in the context of the electrochemical environment. Membranes exhibiting promising properties are being studied as integral components of electrochemical engineering systems. The information obtained from these studies further advances the scientific basis for designing membranes and catalyst layers for electrochemical systems.
Proton/Cation Conducting Polymers
Several projects are under way involving the synthesis of novel membranes comprising block copolymers of sulfonated monomers. An example of this work is provided in the manuscript “Highly Stable, Low Gas Cross-Over, Proton-Conducting Phenylated Polyphenylenes”, Angewandte Chemie, 129 (2017) 9186–9189.
Sulfonated branched oligophenylenes and polyphenylenes
In situ polarization (left axis, solid), power density (right axis, open), under H2/O2. Conditions: 80 °C, 100% RH, 0.5/1.0 slpm anode/cathode gas flows, zero back-pressure. sPPB and sPPN are experimental membranes
Hydroxide/Anion Conducting Polymers
A major effort is under way involving the synthesis of caustic-stable anion conducting polymers and membranes. Examples of this work include
"Cationic Polyelectrolytes, Stable in 10 M KOHaq at 100 ˚C", ACS, Macro Letters 6(2017) 1089. Here, we report on poly(arylene-imidazoliums), which were synthesized by microwave polycondensation of dialdehyde with bisbenzil and quantitatively functionalized by alkylation. This cationic polyelectrolyte is sterically protected around the C2-position and is stable in 10 M KOHaq at 100 ˚C (t1/2 of >5000 h). Alkaline stability is rationalized through analyses of model compounds, single crystal x-ray diffraction, and density functional theory. The polyelectrolytes form tough, pliable, transparent, ionically conductive films.
“Hexamethyl-p-Terphenyl Poly(benzimidazolium): A Universal Hydroxide-Conducting Polymer for Energy Conversion Devices”, Energy & Environmental Science, 9 (2016) 2130 - 2142. A hydroxide-conducting polymer, HMT-PMBI, which is prepared by methylation of poly[2,2’-(2,2’’,4,4’’,6,6’’-hexamethyl-p-terphenyl-3,3’’-diyl)-5,5’-bibenzimidazole] (HMT-PBI), is utilized as both the polymer electrolyte membrane and ionomer in an alkaline anion-exchange membrane fuel cell and alkaline polymer electrolyzer. A fuel cell operating between 60 and 90 °C and subjected to operational shutdown, restarts, and CO2-containing air, demonstrates remarkable in situ stability for >4 days, over which its performance improved over time. The ease of synthesis, synthetic reproducibilty, scale up, and exceptional in situ and ex situ properties of HMT-PMBI renders this a potential benchmark polymer for energy conversion devices requiring an anion-exchange material.